The present invention relates to fluids employed in subterranean operations, and more particularly to fluids with formation stimulation capability and methods of their use during drill-in and completion operations.
Drill-in fluids are specially designed for drilling through a subsurface hydrocarbon reservoir portion of a wellbore. Such fluids are generally formulated to minimize formation damage and maximize production of the zones exposed by the drilling. Formation damage can occur through many different mechanisms including, for example, emulsion blocks, water blocks, polymer/filtrate/particle invasion, precipitates, improper wetting of the formation, and the like. The damage may be remediated by stimulating the formation in the form of fracturing, acidizing or improving flow-back with chemical treatments. Many drill-in fluids are aqueous-based to reduce formation damage such as oil-wetting and/or emulsion blockages in the formation. Drill-in fluids may be specifically formulated as brines containing solids, such as calcium carbonate, of appropriate particle size and may contain various polymers along with the penetrated rock fragments generated by the drill bit. Few additives beyond those for filtration control and carrying cuttings, however, are typically present in a drill-in fluid. Similar fluids may be employed during well completion operations. Indeed, drill-in fluids and completion fluids with or without solids are typically similar in design.
Completion fluids are designed to facilitate final operations prior to initiation of production, such as setting screen production liners, packers, downhole valves or shooting perforations into the producing zone. The fluid is generally designed to control a well in the event of downhole hardware failure, without damaging the formation or completion components. Completion fluids, like drill-in fluids are typically brines (e.g., chlorides, bromides and formates), although any fluid of proper density and flow characteristics may be employed. The fluids are typically selected to be chemically compatible with the formation and formation fluids, and are frequently filtered prior to use to avoid introducing undesirable or non-degradable solids at the near-wellbore area.
Stimulation treatment to improve oil and/or gas recovery and well producibility is typically performed after drill-in operations and/or after performing well completion operations in a target reservoir section of the formation. Such stimulation treatments may include fracturing, acidizing, or other chemical treatments to improve connectivity to the wellbore. Because they occur as separate operations after drill-in and/or completion operations, stimulation treatments require special equipment, can be expensive, and delay the time for the well to come online.